Abstract Base Classes

Intermediate Object-Oriented Programming in Python

Jake Roach

Data Engineer

Abstract base classes

Abstract base classes create a blueprint for classes by defining abstract methods that must be implemented by all children

Ensures common behavior for a group of classes
@abstractmethod decorator
Meant to be inherited, not instantiated
Not all methods in abstract base class must be abstract (concrete methods)

class School:
    # Do things such as enroll 
    # and add a course

class MiddleSchool:
    # Play an instrument, join a club
    # but must enroll and add courses

class HighSchool:
    # Play a varsity sport, apply
    # for college, but must enroll 
    # and add courses

Creating an abstract base class

from abc import ABC, abstractmethod


# Create an abstract base class that inherits
# from ABC
class School(ABC):
    @abstractmethod
    def enroll(self):
        # This method must be implemented
        # in classes that inherit from it
        pass


    # Concrete methods are inherited
    def graduate(self):
        print("Congrats on graduating!")

Inherit from the ABC class in the abc module
pass
Any class that inherits School must implement the enroll() method
Can also implement concrete methods

Implementing abstract base classes

class HighSchool(School):
    def enroll(self):
        print("Welcome to high school!")

# Create an instance of HighSchool
high_school = HighSchool()
high_school.enroll()

Welcome to high school!

high_school.graduate()

Congrats on graduating!

HighSchool must define an enroll() method
TypeError if enroll() is not defined
HighSchool inherits the graduate() method

Multiple abstract methods

class School(ABC):
    @abstractmethod
    def enroll(self):
        pass

    @abstractmethod
    def add_course(self, course_name):
        pass

    def graduate(self):
        print("Congrats on graduating!")

Two abstract methods, enroll() and add_course()

class HighSchool(School):
    def __init__(self):
        self.courses = []

    # Implementing abstract method
    def enroll(self):
        print("Welcome to high school!")

    # Implementing abstract method
    def add_course(self, course_name):
        self.courses.append(course_name)
        print(f"You enrolled in {course_name}")

Let's practice!

Intermediate Object-Oriented Programming in Python